With the changes in dietary culture and lifestyles over the recent years, an increasingly large number of people are receiving dental treatment. Dental experts often warn of the necessity of regular checkups and early treatment of teeth. When dental treatment is performed, in many cases, roentgenography for examining the state of teeth (dentition) and gums is performed. Conventionally, roentgenography mostly involves acquisition of a localized projection image of a gum area using X-ray film. As an alternative method to roentgenography or a method concomitantly used therewith, an X-ray computed tomography (CT) scanner, a dental panoramic imaging apparatus dedicated to dentistry, or the like is used.
The X-ray CT scanner merely applies a typical CT imaging method to the imaging of the jaw portion. The resolution of a panoramic image along the dentition that has been reconstructed from images acquired by the scanner is not very high. The X-ray CT scanner is limited for use in examination of the overall dentition.
Meanwhile, in the dental panoramic imaging apparatus, an X-ray source and X-ray detector pair is positioned so as to sandwich the jaw portion of a subject therebetween. The pair is then moved around the jaw portion, and radiolucency data is collected. A panoramic image along a predetermined cross-section in relation to the dentition is generated from the collected data. The dental panoramic imaging apparatus includes an analog-type panoramic imaging apparatus that uses film and developers, and a digital-type panoramic imaging apparatus that uses an imaging plate, such as a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS).
A typical digital-type panoramic imaging apparatus is provided with a revolution driving means. The revolution driving means integrally revolves an X-ray source and an X-ray image detecting unit around a subject. The X-ray source and the X-ray image detecting unit are disposed such as to oppose each other with the subject therebetween. The X-ray source includes an X-ray tube and a collimator that narrows the X-ray irradiated (or emitted) from the X-ray tube into a split-beam state. The X-ray image detecting unit includes an X-ray detector, such as an X-ray CCD or CMOS sensor. The X-ray detector outputs an electrical signal in digital quantity that is based on an incident X-ray quantity. Furthermore, the panoramic imaging apparatus includes a storage means and an image processing means. The storage means successively stores therein image information collected by the X-ray detector as frame images. The image processing means successively reads out the image information from the storage means at a predetermined time interval. The image processing means adds the pieces of image information that have been read out, while shifting each piece of image information by a predetermined distance, in relation to the direction in which an image moves over the continuous pieces of image information. The image processing means thereby forms a panoramic image of an arbitrary cross-section, based on the read-out interval and the amount of shifting of the pieces of image information. This image formation method is also referred to as a tomosynthesis method. As a result, a panoramic image of a cross-section along the dentition of a patient can be provided as an image for diagnosis on a monitor, such as a personal computer, without the use of X-ray films.
Meanwhile, periodontal disease refers to disease that occurs in the periphery of the teeth, that is, the gingiva, alveolar bone, periodontal membrane, or the cementum portion under the surface of the tooth root. However, in general, periodontal disease refers to an inflammatory disease that occurs around a tooth and is caused by bacteria, such as porphyromonas gingivalis. More than 90 percent of patients have this type of periodontal disease. Therefore, the present invention, described hereafter, also primarily targets the typical type of periodontal disease. The typical type of periodontal disease is referred to, hereafter, as “periodontal disease” and is differentiated from other types of periodontal disease.
To start treatment of periodontal disease, first, an examination is conducted to discover the current state of symptoms, that is, the extent of progression of the symptoms. A diagnosis is then made regarding the symptoms that will result. Various methods have been developed up to now. The primary examination methods today include a method that involves probing, an examination method in which dental X-rays are used, and an examination method in which microbial examination is used. Furthermore, when an examination is conducted, individual differences in the aspects of dental roots and alveolar bone, individual differences in dental bite, and the like also need to be considered.
The probing examination method is a method in which a probe (examination exploratory probe) is inserted into a pocket that is formed around a tooth. The state of symptoms is explored while measuring the depth of the pocket. The probing examination method is the simplest method and superior in terms of being applicable to all stages of symptoms. However, the examination results differ based on the skills of the technician, the anatomical aspects of the teeth, the attachment of tartar, and the like. In addition, when inflammation of the bottom portion of the periodontal pocket is severe, a problem occurs in that the probe damages the tissue in the bottom portion of the periodontal pocket and the patient experiences pain. That is, the depth of the pocket is measured by the probe (the probe for examination, and specifically, a calibrated probe referred to as a pocket probe) being inserted until the bottom portion of the pocket is reached. However, measurement is taken at about six sites for a single tooth and may be accompanied by bleeding. The examination causes the patient pain and is troublesome. Furthermore, even when the depth of the pocket is the same, the volume of the tooth below the pocket differs depending on the tooth and the individual. Therefore, the strength supporting the tooth cannot be determined by the depth of the tooth alone. A problem occurs in that the depth of the pocket is insufficient as an objective indicator of periodontal disease.
The examination method in which dental X-rays are used is a method in which bone level and outer shape of the alveolar bone are grasped from an X-ray photograph of a tooth and periodontal tissue, and examined. This method is superior to the probing method, in which measurement error is an issue, in that resorption of the alveolar bone and the outer shape of the alveolar bone can be accurately read. However, this method cannot be used at an early stage of periodontal disease and cannot be used often. In addition, in many cases, the dental X-ray images are unclear. A problem occurs in that accuracy may decrease.
The examination method in which microbial examination is used is a method in which the bacteria causing a periodontal infection is examined. The activity and progression of periodontal disease are examined. That is, the strength of pathogenicity is thought to differ depending on the bacteria strain. Disease activity is determined through identification of the bacteria strain. However, a problem occurs in that the identification of bacteria strain is time-consuming and costly, and the accuracy of prediction of disease activity (progression and recurrence of periodontal disease) is not very high.